The present invention relates generally to electrical machinery and, in particular, to a method of winding motors and other electrical machinery having windings with multiple wire strands that in turn reduces AC or proximity losses and prevent overheating.
Electrical machinery of the type having multiple windings has been in development for over a century. A vast array of electromechanical rotating machinery has become available, including various types of AC and DC motors, generators, and other equipment for both single-phase and multi-phase operation.
In winding the armatures and field coils for such machines, it is common practice to pack the windings as tightly as possible to achieve the greatest amount of conductor density for a given cross-section. However, the same amount of attention is has not been given to the precise way in which the various strands are laid into their respective slots. In conventional electric machine windings, the conductors are randomly distributed within the slots, and are typically referred to as xe2x80x9crandom windings.xe2x80x9d FIGS. 1 and 2 show examples of random windings having multiple wire strands per turn, with FIG. 1 illustrating the particular case of a single layer winding, and FIG. 2 illustrating a double layer winding utilizing an insulating layer to one or more phases. In these drawings, the number in each wire indicates the number of the turn to which that wire strand belongs.
FIGS. 1 and 2 are not meant to depict any electrical machine in particular, but rather, are intended to present the cross-section of a typical arrangement wherein, notably, the strands of one winding are intermingled in random fashion with the strands of another, resulting in an uncontrolled distribution between the strands of one winding and the strands of another. Although, as shown in FIG. 2, the insulating layer provides a barrier between the phases, the strands of each winding are still randomly distributed within each phase.
Although it is well known that losses may occur through self-induction when conductors carrying dissimilar currents are maintained in close proximity to one another, the precise affect of randomly distributed multi-strand windings in electrical machinery has not been known or predictable. This is due to the fact that, in the absence of advanced investigative techniques such as finite-element analysis (FEA), it has heretofore been impossible to precisely determine the source(s) of such losses.
In addition, particularly with respect to certain rotating machinery, the width-to-length ratio associated with the slots used to hold the windings has not been as pronounced. In particular, whereas in the past this ratio has been on the order of 2:3, very deep narrow slots are being used to increase efficiency, and this increases the likelihood that the strands may be randomly distributed with respect to the depth of the slot, thereby exacerbating the proximity effect. Furthermore, higher frequency machines are being designed, which manifests as an increase in the ratio of AC resistance to DC resistance.
Broadly, and in general terms, the present invention utilizes non-random windings to reduce the proximity effect in electrical machines, including rotating machines such as various types of motors. That is, to reduce the proximity effect, and the additional losses and overheating associated therewith, a method of the invention abandons the random winding technique used for decades in the construction of standard industrial electric motors in favor of a more controlled arrangement.
Thus, with respect to electrical machinery of the type wherein multi-strand electrical wiring is received within a slot relative to a surface associated with the transmission of magnetic flux, a method of dressing the wiring within the slot according to the invention includes the step of winding the strands of each turn in one or more layers, each layer being substantially parallel to the surface associated with the transmission of magnetic flux. The winding may be a multi layer winding, in which case the turns associated with each layer are preferably separated by an insulating layer. The invention is applicable to various types of machines and motors, including AC, brushless DC and variable reluctant (VR) types. The conductors may be of a circular cross section or other geometry, such as flattened tapes.